This application claims the benefit of a Japanese Patent Applications No.2002-164111 filed Jun. 5, 2002 and No.2003-153182 filed May 29, 2003, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to adaptive antenna units, and more particularly to an adaptive antenna unit which adaptively controls transmission and reception characteristics by arranging a plurality of antenna element pairs each made up of a feeding antenna element and a plurality of parasitic antenna elements, and an adaptive antenna unit which adaptively controls transmission and reception characteristics by arranging a plurality of array antenna sections each formed by a plurality of feeding antenna elements. The present invention also relates to a terminal equipment which is provided with such an adaptive antenna unit.
2. Description of the Related Art
Various kinds of adaptive antenna units having a plurality of antenna elements have been proposed. For example, a diversity antenna unit, having a plurality of antenna elements arranged so as to reduce respective spatial correlations, is known.
FIG. 1 is a diagram showing an example of such a conventional diversity antenna unit. The diversity antenna unit shown in FIG. 1 includes a plurality of antenna elements 31, a plurality of transmitter-receiver radio frequency front ends (RFF/Es), a plurality of transmitter-receivers (T/Rs) 33, and a digital signal processing circuit 34. The digital signal processing circuit 34 includes a weighting control circuit 35, a plurality of weighting circuits 36, and a combining (Σ) circuit 37.
The antenna elements 31 are arranged at a pitch d satisfying a relationship d>λ, where λ denotes the wavelength. In other words, the antenna elements 31 are arranged so as to reduce the spatial correlations thereof. One RFF/E 32 and one transmitter-receiver 33 are provided with respect to each antenna element 31. A reception signal received by the antenna element 31 is weighted by the corresponding weighting circuit 36 via the RFF/E 32 and the transmitter-receiver 33. The weighting circuit 36 corresponding to each antenna element 31 is controlled by the weighting control circuit 35, so as to maximize a signal-to-interference-plus-noise ratio (SINR) of an output signal of the combining circuit 37. The output signal of the combining circuit 37 is obtained by combining the weighted reception signals obtained via the weighting circuits 36.
FIG. 2 is a diagram for explaining a transmitter-receiver circuit corresponding to one antenna element 31. The transmitter-receiver circuit shown in FIG. 2 includes one RFF/E 32 and one transmitter-receiver (T/R) 33 respectively corresponding to one antenna element 31 shown in FIG. 1, and the digital signal processing circuit 34 which is formed by a digital signal processor (DSP).
The RFF/E 32 includes a transmitter-receiver shared unit 40, bandpass filters (BPFs) 41, 43 and 46, low-noise amplifiers (LNA) 42 and 44, and a power amplifier (PA) 45. The transmitter-receiver share unit 40 includes a switch and a filter to enable sharing of the antenna element 31 for the transmission and the reception.
The transmitter-receiver 33 includes a mixer 47, a bandpass filter (BPF) 48, demodulators 49 and 50, lowpass filters (LPFs) 51 and 52, analog-to-digital converters (ADCs) 53 and 54, digital-to-analog converters (DACs) 55 and 56, lowpass filters (LPFs) 57 and 58, modulators 59 and 60, a combining (+) circuit 61, and local oscillators LO1 through LO3.
The RFF/E 32 eliminates by the BPF 41 an unwanted band component of the reception signal received by the antenna element 31 and obtained via the transmitter-receiver shared unit 40. An output of the BPF 41 is amplified by the LNA 42 and input to the transmitter-receiver 33 via the BPF 43. In addition, the RFF/E 32 amplifies by the LNA 44 the transmission signal received from the transmitter-receiver 33. An output of the LNA 44 is amplified by the PA 45 to a desired transmission power. An output of the PA 45 is input to the BPF 46 which eliminates an unwanted band component, and an output of the BPF 46 is input to the antenna element 31 via the transmitter-receiver shared unit 40 and is transmitted from the antenna element 31.
In the transmitter-receiver 33, the mixer 47 mixes the output of the BPF 43 and a local oscillation signal from the local oscillator LO1 to output an intermediate frequency (IF) signal. The BPF 48 eliminates an unwanted band component of the IF signal received from the mixer 47. The demodulators 49 and 50 have structures similar to the mixer 47. Hence, an output of the BPF 48 is mixed with 90-degree phase local oscillation signals from the local oscillator LO2 in the respective demodulators 49 and 50. Outputs of the demodulators 49 and 50 are input to the corresponding LPFs 51 and 52 wherein unwanted high-frequency components are eliminated. Outputs of the LPFs 51 and 52 are converted into digital signals by the corresponding ADCs 53 and 54. The digital signals output from the ADCs 53 and 54 are finally input to the digital signal processing circuit 34, so as to form a reception path.
On the other hand, digital signals output from the digital signal processing circuit 34 are converted into analog signals in the corresponding DACs 55 and 56, and input to the corresponding LPFs 57 and 58 wherein unwanted high-frequency components are eliminated. Outputs of the LPFs 57 and 58 are input to the corresponding modulators 59 and 60 and modulated by 90-degree phase local oscillation signals from the local oscillator LO3. Outputs of the modulators 59 and 60 are combined in the combining circuit 61 and finally input to the RFF/E 32, so as to form a transmission path.
The antenna elements 31 shown in FIG. 1 may be arranged at a pitch d satisfying a relationship d<λ, where λ denotes the wavelength, so as to increase the spatial correlations thereof. In this case, an adaptive antenna unit, which is often referred to as an array antenna unit, is formed. The structures of the RFF/Es 32 and the transmitter-receivers 33 for the adaptive antenna unit are the same as those shown in FIGS. 1 and 2.
In the case of the diversity antenna unit having the antenna elements 31 arranged so as to reduce the spatial correlations, a grating lobe is generated by the spreading of the pitch of the antenna elements 31. For this reason, there are problems in that the gain in a desired direction decreases, and that radio wave is also radiated in a direction other than the desired direction at the time of the transmission.
On the other hand, in the case of the array antenna unit having the antenna elements 31 arranged so as to increase the spatial correlations thereof, the gain in the desired direction improves because no grating lobe is generated. However, since the pitch of the antenna elements 31 is narrow, it is difficult to compensate for the fading and to separate a desired wave and an interference wave with adjacent arrival directions.
Accordingly, a structure which combines diversity branches and array branches, as shown in FIG. 3, has been proposed. In FIG. 3, those parts which are the same as those corresponding parts in FIGS. 1 and 2 are designated by the same reference numerals.
The antenna unit shown in FIG. 3 includes a plurality of array branches a1 through an, and a signal processing circuit 34, An array branch ai includes a plurality of antenna elements 31-i, a plurality of RFF/Es 32-i, and a plurality of transmitter-receivers (T/Rs) 33-i, where i is an integer satisfying i=1 to n. The digital signal processing circuit 34 includes a weighting control circuit 35, a plurality of weighting circuits 36-1 through 36-n, and a combining (Σ) circuit 37.
In each array branch ai, the antenna elements 31-i are arranged at a pitch d1 satisfying a relationship d1<λ, where λ denotes the wavelength. In addition, the array branches a1 through an are arranged at a pitch d2 satisfying a relationship d2>λ, where λ denotes the wavelength, so as to form a diversity branch structure.
In the digital signal processing circuit 34, the weighting control circuit 35 controls the weighting of each of the weighting circuits 36-1 through 36-n respectively corresponding to the antenna elements 31-1 through 31-n of the corresponding array branches a1 through an, so that the SINR of an output of the combining circuit 37 becomes a maximum.
The fading compensation and the like are carried out by the diversity combining process, and the separation of the desired wave and the interference wave with adjacent arrival directions is carried out by the diversity branches. In a case where a high-gain directivity is to be obtained in the desired direction, it is possible to cope with various states by applying an adaptive control by the array branches a1 through an, as proposed in an International Publication Number WO00/03456 A1, for example.
According to the structure shown in FIG. 3, for example, one RFF/E 32-i, one transmitter-receiver 33-i, and one weighting circuit 36-i are required with respect to each antenna element 31-i, where i=1 to n. In addition, each transmitter-receiver 33-i includes demodulators, modulators, ADCs, DACs and the like as shown in FIG. 4. For this reason, when the number of antenna elements is increased in order to improve the transmission and reception characteristics, there were problems in that the antenna unit as a whole becomes bulky, and that the power consumption of the antenna unit increases considerably. Consequently, such a bulky and power-consuming antenna unit was unsuited for mobile terminals which are used for mobile communications.